This invention relates to motion detection apparatus in a video signal processing system.
The invention is applicable to varied video processing systems including means for delaying video signals by field intervals or greater. However, the invention will be described in the environment of a video tape recorder, VTR.
In magnetic recording, the quality of the recorded medium generally determines the duration and occurrence rate of dropouts or signal defects which cause information gaps or voids during replay. Defects on the recorded medium along tracks travelled by transducer heads when recording or replaying information are the cause of such dropouts. One example of such a defect is the stipples or bumps of magnetic oxide which occur periodically on a magnetic recorded medium. The stipples cause the transducer heads to bounce off the recorded medium and thereby result in the information gaps while the transducer heads are removed from the recorded medium.
Gaps in the record and replay information due to dropout always present a problem, especially when the recorded information is video. Many techniques have been devised for coping with the problem of video dropout during replay by replacing the missing dropout information with information derived through an analysis of the recorded information in close proximity to the missing dropout information. In one simple technique, the location of missing or dropout information in any field or frame is sensed and replaced with information from the same field or frame having a high probability of being similar to the missing information. The replacement information is continuously derived by circulating the replayed signal through a delay of duration equal to either one or two raster scan lines. As is well known, use of a one line delay requires that a processor be included to change the subcarrier phase of the replacement information, whereas use of a two line delay requires no such processor. When recorded scenes contain only vertical lines, this technique provides exact replacements for missing dropout information. However, such replacements become imperfect when recorded scenes contain diagonal lines. Furthermore, this technique derives replacement information for dropouts of durations greater than one scan line by repeatedly using the information in the delay. This causes an instantaneous disturbance in the replayed signal which appears in a portion of the displayed picture as a vertical smear and is highly visible.
To resolve the difficulties encountered with the technique described above, a field store delay is combined with the raster scan line delay for directly replacing missing dropout information with information from either the raster scan line delay or the field store delay in accordance with the nature of the dropout information. Dropout information is replaced with information from the field store delay when no motion is detected in the picture. Alternatively, dropout information is replaced with information from the line store delay when motion is detected in the picture.
To switch from field to line delayed dropout compensation signals when image motion occurs, it is necessary to detect the occurrence of image motion in the vicinity of dropouts.